The present project has as its primary objective prevention of chemical carcinogen-induced neoplasia of the large intestine. The proposed means of achieving this goal is by the use of antioxidants. Antioxidants with differing degrees of absorption from the gastrointestinal tract will be employed in a effort to obtain compounds that can inhibit activated species of carcinogens in the lumen of the large bowel, in the wall of the large bowel, or at a site remote from the bowel. Primary emphasis will be placed on sulfur-containing antioxidants. Efforts will be made to determine the mechanism of inhibition of compounds having this property. An additional objective of the project will be to determine if compounds currently present in the environment can inhibit the occurrence of carcinogen-induced neoplasia of the large bowel. These include a number of pesticides chemically related to disulfiram and diethyldithiocarbamate, two compounds previously shown to inhibit dimethylhydrazine-induced neoplasia of the large bowel. Also to be studied are lignins which are high molecular weight polyphenolic plant constituens with antioxidant activity.